In[19]:=
Clear[Eternity,x];
Eternity[x_]:=Eternity[x];
In[21]:=
Clear[EmptyQ];
EmptyQ[{}]:=True;
EmptyQ[x_List]:=False;
EmptyQ[x_]:=Print["Argument to EmptyQ must be a list."];
This below works for the empty list it gives 0.
In[25]:=
Clear[length,list]
Function[length,
Function[list,If[EmptyQ[list],
0,
1 +
length[Rest[list]]]]][
Eternity][{}]
Out[26]=
0
What I am trying to do here is pass the function above as the
definition of the parameter MkLength and then run the exactly the same
thing by MkLength[Eternity].
It doesn't work.
In[27]:=
Function[MkLength,MkLength[Eternity][Function[length,
Function[list,If[EmptyQ[list],0,1 +
length[Rest[list]]]]]]][{}]
Out[27]=
{}[Eternity][
Function[length,Function[list,If[EmptyQ[list],
0,1+length[Rest[list]]]]]]
But look what happens when I use the function abbreviation instead of
Function[MkLength........
In[29]:=
#[Eternity]&[Function[length,
Function[list,If[EmptyQ[list],0,1 + length[Rest[list]]]]]]
[{}]
Out[29]=
0